The present invention relates to disposable absorbent articles such as baby diapers or sanitary napkins having a breathable yet liquid leakage retarding backsheet which comprises an inner and an outer layer. The inner layer being closer to the absorbent structure of the article is a formed film with directional liquid transport characteristics while the outer layer is a fibrous fabric.
Disposable absorbent articles such as baby diapers, adult incontinence products, sanitary napkins and panty liners are well known in the art. These articles have a wearer facing side through which they typically absorb liquids discharged by the wearer. The liquid is stored in an absorbent structure. Liquid leakage from the article through the surface opposite the wearer facing side is usually prevented by incorporating a liquid impermeable backsheet on that side.
It is also well established in the art that a backsheet allowing gaseous fluid (air) communication with the environment, usually referred to as breathability, is highly desirable. Breathability improves with the amount of air permeating through a backsheet. This amount is proportional to the open area (the sum of the area of all apertures) in the backsheet. Obviously too many and particularly too large apertures in the backsheet lead to compromising the liquid leakage prevention, which is the primary function of a backsheet.
Many suggestions how to provide breathable backsheets have been recorded in the art. Numeral attempts of combining the mutual contradicting features of gas permeability and liquid impermeability have been documented in patents and patent applications. However the lack of commercially available breathable disposable absorbent articles indicates that the technology so far suggested has not provided an all around satisfactory result for the desired technical requirements at commercially acceptable condition. More often than not satisfaction of one desired feature went to such an extreme that the respective other feature was not properly satisfied any longer.
For example sanitary napkins with very high breathability at the cost of frequent liquid leakage (leading to soiling of the undergarments of a wearer) cannot be considered satisfactory. On the other hand satisfying the liquid leakage problem properly usually resulted in almost impermeable, that is non-breathable, backsheets. In particular microporous films which have no macroscopic apertures are not liquid permeable. But microporous films only allow air communication by diffusion which is an order of magnitude less than the achieved breathability with the current invention.
Good progress has been made in the field of formed films having directional liquid transport wherein liquid transport over a certain pressure drop across a formed film is better in one direction versus the other. These so called one way formed film materials have found wide usage as liquid permeable topsheets after being treated with surfactant in the field of sanitary napkins and panty liners, but also for diapers and incontinence products. Alternative topsheets of fibrous fabric polymers typically have no directional liquid transport. They are also treated with surfactant but have an intrinsic hydrophobic behaviour when being used as topsheets for absorbent articles after the surfactant has worn off.
Combinations of breathable and liquid permeable sheets in order to provide a certain liquid impermeability while satisfying the desire for breathable backsheets have already been suggested for example in U.S. Pat. No. 3,881,489. In this disclosure a breathable backsheet is provided by confining an outer layer of formed film material having surface aberrations with apertures therein and an inner layer of a paper tissue having a high void volume and having been made hydrophobic by impregnating it with a paraffin wax. This document does not disclose the desire for using a directional liquid transport type polymeric film structure with a hydrophobic fibrous fabric layer made of polymeric material.
Other prior art attempts to provide breathable backsheet assemblies comprising more than one layer are e.g. documented in U.S. Pat. No. 4,341,216, EP-A-109 126 or EP-A-203 821. Neither of these disclosures provides constructions of breathable backsheets similar to the present invention.
Single layer breathable backsheets are known for example from GB-A-2184391, GB-A-2184390, GB-A-2184389, U.S. Pat. Nos. 4,591,523, 4,839,216 or EP 156471.
In PCT publication WO 9309744 absorbent articles which have a hybrid topsheet are disclosed. The hybrid topsheet comprises a non-woven fabric overlaid by a formed film were the non-woven fabric is folded around the edges but not fully covering the second surface of the formed film. This structure is used as the topsheet to facilitate a liquid absorption in contrast to breathability. However it would of course provide breathability if it was left in air communication with the environment. This disclosure teaches to use the structure as a topsheet which is typically rendered hydrophilic. Further the disclosed topsheet structure has a formed film outer layer and a non-woven inner layer in respect to the absorbent structure. Therefore this publication also does not disclose the structures according to the present invention.
In unpublished, pending applications U.S. Ser. Nos. 08/042,364; 08/042,365 and 08/042,345 all filed on Feb. 4, 1993 other topsheets comprising a formed film and non woven fabric are disclosed. However these constructions are rendered hydrophilic for the purpose of using them as topsheets receiving liquid to be transported towards the absorbent core rather than to use them on breathable backsheets.
It has now been found that combining a gas permeable, hydrophobic, polymeric fibrous fabric and an apertured formed film having a directional liquid transport phenomena provides a particularly desirable breathable backsheet. Backsheets according to this construction have exceptionally good breathability due to the large open area and the combination of formed film and fibrous fabric allows to select the layers so as to provide the desired liquid leakage retarding function. Therefore the present invention provides an non-leaking breathable backsheet and absorbent articles comprising this backsheet.
It is therefore an objective of the present invention to provide absorbent articles in particular sanitary napkins or panty liners having a superior breathability as defined by free gas permeability of the backsheet while simultaneously retarding liquid leakage through that backsheet to such an extend that the user of such products does not experience a recognisable difference between a liquid impermeable backsheet and the breathable backsheet according to the present invention.
An additional objective satisfied by the present invention is also to provide a backsheet which has a desirable and user preferred fibrous outside surface.
Another patent application is being filed on the same date as this application. It is entitled xe2x80x9cBreathable dual layer backsheet design for disposable absorbent articlesxe2x80x9d by M. Depner and M. Divo and also assigned to xe2x80x9cThe Procter and Gamble Companyxe2x80x9d.